This invention relates to improvements in electro-magnetic valves, particularly for household appliances.
The rapid development of the household appliance industry in the last 30 years has triggered a similar development in the case of accessory parts. Compact type of construction, rational mass production, designs appropriate for the material involved, i.e. designs appropriate for plastics material, and working reliability were what showed the way.
In the field of electro-magnetic valves, without exception the same basic design principle has been used since 1946 see U.S. Pat. No. 2,562,315. All electro-magnetic valves to be found on the market are based on this design principle.
The apparatus of the prior art (see FIG. 1) comprise an electro-magnetic valve having hydraulic pilot control, consisting of a valve body (1) having an inlet (5) and an outlet (6), with a concentric valve seat (10) which is sealable by a flexible diaphragm (2), in which respect both the inlet and the outlet are arranged on one side of the diaphragm; a hydraulic pressure chamber (3) on the other side of the diaphragm; a filling aperture (7) from the inlet (5) to the pressure chamber (3) and a central pressure-relief aperture (11) in the diaphragm (2) from the pressure chamber (3) to the outlet 6; and an electro-magnetic means for opening the pressure-relief aperture, for example, in the form of a moving-coil armature (16).
The electro-magnetic valves to be found on the market nowadays differ merely in design details, but all operate in accordance with the method described in U.S. Pat. No. 2,562,315.
To effect hydraulic closing of the diaphragm, as the fluid flows through the small filling aperture (7) from the inlet (5) into the pressure chamber (3), the flexible diaphragm (2) is pressed onto the valve seat (10). As soon as the moving-coil armature (16) is drawn into the magnet coil (14), fluid emerges from the pressure chamber (3) through the pressure-relief aperture (11) into the outlet (6), the pressure chamber (3) is relieved and the flexible diaphragm (2) is lifted from the valve seat (10) by the water pressure occurring from the inlet (5) and the water flowing through the valve is discharged.
When the current is switched off, the moving-coil armature (16) closes the pressure-relief aperture (11), water flows through the filling aperture from the inlet into the pressure chamber (3), so that the flexible diaphragm (2) is pressed onto the valve seat (10). In this respect it is possible, by correct dimensioning of the filling aperture (7), to bring about a slow closure of the valve, in order to avoid damage by water hammer.
This advantage, as well as the relatively slight actuating forces, have displaced practically all other systems on the market. The main disadvantage of the magnetic valves to be found on the market nowadays is the relatively high electrical power requirement, which on the one hand requires a critical monitoring of the heating of the coils, and on the other hand makes these valves appear to be unsuitable for a direct electronic control.